Sulfur tolerant alumina catalyst support

Abstract

The present invention is directed to an improved catalyst support and to the resultant catalyst suitable for treating exhaust products from internal combustion engines, especially diesel engines. The support of the present invention is a structure comprising alumina core particulate having high porosity and surface area, wherein the structure has from about 1 to about 40 weight percent silica in the form of cladding on the surface area of said alumina core. The resultant support has a normalized sulfur uptake (NSU) of up to 15 μg/m2.

1. A structure comprising alumina core particulate having high porosity of at least about 0.2 cc/g, a surface area of greater than 20 m 2 /g and having silica cladding on the surface area of said alumina core, wherein the structure has from about 1 to about 40 weight percent silica and has a normalized sulfur uptake (NSU) of up to 15 μg/m 2 . 
     
     
       2. The structure of  claim 1  wherein the particulate comprising alumina core having an average particle size of from 1 to 200 μm and a BET surface area of from about 20 to 400 m 2 /g. 
     
     
       3. The structure of  claim 2  wherein the particulate comprising alumina core having a BET surface area of from 100 to 300 m 2 /g and a nitrogen pore volume of from 0.2 to 2 cc/g. 
     
     
       4. The structure of  claim 1  wherein the structure is composed of particulates having an average particle size of from 1 to 10 mm and a BET surface area of from about 20 to 400 m 2 /g. 
     
     
       5. The structure of  claim 1 ,  2 ,  3  or  4  wherein the alumina core further comprises up to about 10 weight percent of a dopant with respect to said alumina. 
     
     
       6. The structure of  claim 5  wherein said structure has from about 8 to 15 weight percent silica cladding and has a NSU of less than 10 μg/m 2 . 
     
     
       7. A catalyst composition, comprising a structure of  claim 5  having a catalytic amount of a noble metal substantially uniformly distributed thereon. 
     
     
       8. The catalyst of  claim 7  wherein the noble metal comprises platinum, palladium or mixtures thereof. 
     
     
       9. The structure of  claim 1 ,  2 ,  3  or  4  wherein the core comprises an alumina selected from the group consisting of bayerite, boehmite, gibbsite, gamma-alumina, delta-alumina, theta-alumina and mixtures thereof. 
     
     
       10. The structure of  claim 9  wherein the alumina core comprises gamma-alumina. 
     
     
       11. The structure of  claim 10  wherein the silica cladding comprises from 5 to 30 weight percent of the structure. 
     
     
       12. The structure of  claim 10  wherein the silica cladding comprises from 8 to 20 weight percent of the structure. 
     
     
       13. The structure of  claim 10  wherein said structure has from about 8 to 15 weight percent silica cladding and has a NSU of less than 10 μg/m 2 . 
     
     
       14. A catalyst composition comprising a structure of  claim 10  having a catalytic amount of a noble metal substantially uniformly distributed thereon. 
     
     
       15. The catalyst of  claim 14  wherein the noble metal comprises platinum, palladium or mixtures thereof. 
     
     
       16. The structure of  claim 9  wherein the silica cladding comprises from 5 to 30 weight percent of the structure. 
     
     
       17. A catalyst composition comprising a structure of  claim 16  having a catalytic amount of a noble metal substantially uniformly distributed thereon. 
     
     
       18. The catalyst of  claim 17  wherein the noble metal comprises platinum, palladium or mixtures thereof. 
     
     
       19. The structure of  claim 9  wherein the silica cladding comprises from 8 to 20 weight percent of the structure. 
     
     
       20. A catalyst composition comprising a structure of  claim 19  having a catalytic amount of a noble metal substantially uniformly distributed thereon. 
     
     
       21. The catalyst of  claim 20  wherein the noble metal comprises platinum, palladium or mixtures thereof. 
     
     
       22. The structure of  claim 9  wherein said structure has from about 8 to 15 weight percent silica cladding and has a NSU of less than 10 μg/m 2 . 
     
     
       23. A catalyst composition comprising a structure of  claim 1 ,  2 ,  3  or  4  having a catalytic amount of a noble metal substantially uniformly distributed thereon. 
     
     
       24. The catalyst of  claim 23  wherein the noble metal comprises platinum, palladium or mixtures thereof. 
     
     
       25. A process for forming an alumina particulate structure useful as a support component for emission control noble metal catalysts comprising forming an aqueous slurry comprising from 5 to 50 weight percent of alumina particulate; heating said slurry to a temperature of 50 to 100° C.; contacting said slurry with an aqueous solution having from 5 to 30 weight percent of a water-soluble silicate to form a mixture thereof; maintaining said mixture at a temperature of 50° to 100° C. for a period of from 1 to 120 minutes; substantially uniformly adding a water-soluble acid to said mixture to achieve a pH of 7.5 over a period of from 5 to 240 minutes from commencement of the acid addition and any further amount of acid sufficient to cause the resultant mixture to have a pH of from 5 to 8; and separating and recovering a dried powder product comprising a high surface area alumina core having from 1 to 40 weight percent of silica in the form of a cladding thereon. 
     
     
       26. The process of  claim 25  wherein the water-soluble silicate is contacted with the aqueous slurry of alumina in amounts to provide a weight ratio of silicate (as SiO 2 ) to alumina of from 1:99 to 40:60. 
     
     
       27. The process of  claim 25  or  26  wherein the water-soluble acid is selected from at least one inorganic mineral acid, is uniformly introduced to provide a pH of 7.5 during the time period of 30 to 60 minutes from commencement of addition and the resultant mixture has a pH of from 7 to 8. 
     
     
       28. The process of  claim 27  wherein the alumina particulate of the slurry has a BET surface area of at least 20 m 2 /g, an average particle size of from 1 to 200 μm, and has a deposit therein in from 0 to 10 weight percent; the water-soluble silicate is selected from alkali metal silicate at a concentration of from 10 to 30 weight percent of said solution; the separating comprises of washing the resultant mixture with an agent selected from the group consisting of ammonium salt of nitrate, sulfate carbonate, hydroxide or chloride; and calcining the resultant product at a temperature of from 400 to 1000° C. 
     
     
       29. The process of  claim 25  or  26  wherein the silicate is an alkali metal silicate and the separating comprises washing to remove the alkali metal from the mixture and drying. 
     
     
       30. The process of  claim 25  or  26  wherein the alumina particulate of the slurry has a BET surface area of at least 20 m 2 /g, an average particle size of from 1 to 200 μm, and has a dopant therein in from 0 to 10 weight percent; the water-soluble silicate is selected from alkali metal silicate at a concentration of from 10 to 30 weight percent of said solution; the separating comprises of washing the resultant mixture with an agent selected from the group consisting of ammonium salt of nitrate, sulfate carbonate, hydroxide or chloride; and calcining the resultant product at a temperature of from 400 to 1000° C.